An uninterruptable power supply device is commercially available and is described, for example, in the Siemens Prospectus "Statische unterbrechungsfreie Stromversorgungen" (Solid-state uninterruptable power supplies) entitled "USV Reihe 42 Leistungsbereich 10 bis 500 kVA" (Series 42 UPS, power range 10 to 500 kVA), Order No. E20001-P161-A4.
FIG. 1 shows a simplified, summary circuit diagram of such an uninterruptable power supply device 2 (UPS device) This UPS device 2 comprises a voltage intermediate circuit converter 4, which includes a component rectifier 6, voltage intermediate circuit 8 and invertor 10. In addition, the UPS device 2 also has the following components: mains commutation inductor L10, mains reset device 12, output filter 14, control device 16 for the converter 4, control device 18 for the mains reset device 12, rectifier input switch Q10, manual bypass switch Q50, mains reset device switch Q51, DC busbar connections C and D, mains connections U1, V1, W1 of the rectifier 6, mains connections U2, V2, W2, N of the mains reset device 12, connections U3, V3, W3, N for a load, connections U4, V4, W4, N for a parallel block, a control panel 20, a monitoring and diagnosis system 22 and remote signalling 24.
A full-wave thyristor three-phase bridge (6-pulse) is provided as the rectifier 6. Optionally, a 12-pulse three-phase bridge can also be provided for the rectifier 6, in order to reduced considerably the mains feedback. For a rating of 500 kVA, the UPS devices are always designed as 12-pulse devices. In the case of the 12-pulse version of the rectifier 6, two balanced 6-pulse three-phase bridges are used, which operate electrically offset through 30.degree. with the aid of a transformer. The control and regulation of the rectifier 6, which is implemented in the converter controller 16, includes the following functions:
software-controlled, battery-conserving automatic charger with IU characteristic and charging current limiting
current limiting to prevent overloading of the rectifier
reduced current limiting and inclined voltage characteristic for operation from a standby mains system
controlled rise: slow voltage and current rise, no inrush current surges
controlled current splitting during parallel operation of two rectifiers in order to prevent nonuniform stresses
staggered rise of the rectifiers in multi-block systems.
The voltage intermediate circuit 8 is designed as a filter circuit. This filter circuit comprises two inductors L11 and a capacitor C20. The two inductors L11 are each integrated in a DC busbar. This filter circuit reduces the natural ripple on the DC voltage and eliminates any voltage spikes. The intermediate circuit voltage is smoothed, and the ripple on the battery current becomes very low. This conserves the battery. The "UPS principle" is based on the fact that the intermediate circuit voltage is kept either by the mains system or in the event of its failure--by the battery in a range which makes it possible for the invertor to keep the output voltage constant.
The invertor 10 comprises a transistor bridge circuit which is connected on the output side to the output filter 14 downstream. This output filter 14 comprises a transformer T20 which has high leakage inductance, and filter capacitors C30. Together with the filter capacitors C30, the leakage inductances of the transformer T20 form the three-phase output filter 14, which filters the fundamental out of the pulse-widthmodulated invertor output voltage and thus produces a sinusoidal output voltage with a low distortion factor. The output voltage is regulated by driving the invertor phases using the method of pulse-width modulation (PWM) with a supersinusoid. Because of the high pulse repetition frequency, the regulation can act very quickly (instantaneous value regulation). Since the waveform of the output voltage is in consequence actively influenced, the feedback effects from loads with non-sinusoidal currents (non-linear load) are also compensated for. This control and regulation of the invertor 10, which is implemented in the converter controller 16, includes the following functions:
voltage regulation with a high dynamic response
current limiting
frequency regulation
phase-angle regulation: exact synchronization with the mains system and with parallel UPS blocks, as a result of which there are no equalization currents and no current surges during changeover processes instantaneous value regulation: low distortion factor on the output voltage even in the case of a non-linear load, high peak currents, active influence on the waveform, high dynamic response pulse forming: the switching state of the power transistors is continuously monitored, no missing pulses possible, optimum utilization of the power section in limit situations.
The mains reset device 12 comprises a three-phase thryristor switch 26, a contactor K50 and a control device 18. The three-phase thyristor switch 26 can take over the load current, without any delay. After a predetermined time interval, the contactor K50 then takes over the continuous current. The mains reset device 12 switches without any interruption in the following cases:
overload on the invertor 10
short circuit
invertor defect
if the invertor 10 is turned off by hand.
The electronic components for control, regulation, protection, monitoring, display and operation can be plugged into a mounting rack and are accommodated on peripheral assemblies relating to their function or components. This electronics section is largely digitized with microprocessors and microcontrollers, SMD, multilayer and hybrid technology being used.
An independent monitoring and diagnosis system 22 is installed in the assemblies required for equipment operation. The display on the control panel 20 provides comprehensive information about the equipment condition and assists fault diagnosis. The system 22 keeps prepared up to date measurements ready to be called up, predicts the expected available battery bridging time using the characteristic method, provides statistical data, continuously stores analogue and digital values, records the processes before and after a defect, detects faults and assists in diagnosis.
The monitoring and diagnosis system 22 includes a battery-buffered process signal memory which continuously records numerous signal states from the UPS equipment. In the event of a fault, the memory process continues for a number of cycles so that the previous and subsequent history of the fault is recorded. The stored operating variables can subsequently be read out.
The display on the control panel 20 offers:
display of the block and system condition
selection of an automatic battery test
display of other up to date measurements and variables derived from them.
The rectifier input and mains reset device input of the UPS device 2 are connected to earth via radio suppression capacitors and are connected between phases and neutral conductors N with varistors (surge arrestors). Together with the LC filter in the voltage intermediate circuit 8, this protects the device against mains overvoltage.
As shown in FIG. 1, the components of the rectifier 6, voltage intermediate circuit 8 and invertor 10 are constructed separately and are arranged in a physically separated manner in the device 2 (interrupted lines). These components have been specifically developed for the application in UPS devices 2. This also applies to the output filter 14, the transformer T20 being special manufacture since it is used both for voltage conversion and for filtering. These components must largely be redeveloped for a new development of a UPS device 2.
Voltage intermediate circuit converters are commercially available for variable speed drives (Siemens Prospectus "Simovert Master Drives", Order No. E20002K4065-A111-A1). These frequency converters from drive technology are available as compact units or flush-mounted units. The compact units are designed in a space-saving "BOOKSIZE" format. They are easily mounted by hooking these compact units into a standard G-rail and using a central screw attachment on the underneath of the unit. The compact and flush-mounted units can be mounted without any gaps between them. This reduces the required switchgear cabinet area. The range of units is designed using a standard connection technique. The mains and DC voltage connections are at the top, and the motor connections generally at the bottom. The new generation of "Simovert Master Drives" equipment comprises a modular system of high-performance components. The components can be used individually for any application. Easy handling, simple mounting, easy wiring and a high level of standardization have been major items in the physical design of the units. This is evident in standardized housings, fastening, connection plane, and the linking of signal and bus lines.
The components are split into system components on the mains side, and system components on the load side. The system components on the main side include the mains commutation inductor and the mains filter. The mains commutation inductor is used to limit mains harmonics. The inductance of the mains commutation inductor reduces the harmonic currents in the converter and feed units as well as the input/return supply units. The effect of the inductor depends on the ratio of the mains short-circuit power to the drive busbar power. The mains filter reduces the radio interference voltages which occur in the converter, feed and input/output supply units to the limits for public mains systems.
The system components on the load side include the output inductor and a harmonic filter. The output inductors can be used to compensate for the active charge-changing currents in long cables. Iron inductors or ferrite inductors may be used. The harmonic filter in each case produces a sinusoidal voltage, which has a low distortion factor, from the pulse-width-modulated output signals from the invertor.